levirate (n.)

custom by which the male next-of-kin of a dead man was bound to marry his widow, 1725, with -ate (2) + Latin levir "brother-in-law," from PIE *daiwer- "husband's brother" (source also of Greek daer, Sanskrit devara, Old English tacor, Old High German zeihhur). Related: Leviratic; leviratical.